Photographic processing apparatus

ABSTRACT

When using unstable processing solutions, high recirculation and/or replenishment rates may be required. However, this may result in non-uniform processing of photographic material in processing apparatus using such solutions. Described herein is apparatus in which agitation members (17) are provided in the processing tank. The members (17) are fixed to a wall (11) of the tank at a location (18). The member (17) has a free end (25) which is positioned to lie against emulsion surface (26) of material (20) being processed (or against inner wall surface (19) if no material (20) is present). As material (20) is moved along path (13).

FIELD OF THE INVENTION

This invention relates to photographic processing apparatus and is moreparticularly concerned with agitation of processing solutions withinsuch apparatus.

BACKGROUND OF THE INVENTION

Conventional colour photographic silver halide materials are processedby a process which includes a colour development step. In this stepsilver halide is reduced to metallic silver in the light-exposed areasand the oxidized colour developer formed in this reaction then coupleswith a colour coupler and forms image dye. The amount of dye produced isproportional to the amount of silver halide reduced to metallic silver.

Redox amplification processes have been described, for example inBritish Patent Specifications GB-A-1268126, GB-A-1399481, GB-A-1403418and GB-A-1560572. In such processes colour materials are developed toproduce a silver image (which may contain only small amounts of silver)and then treated with a redox amplifying solution to form a dye image.The redox amplifying solution contains a reducing agent, for example acolour developing agent, and an oxidizing agent which is more powerfulthan silver halide and which will oxidize the colour developing agent inthe presence of the silver image which acts as a catalyst. Oxidizedcolour developer reacts with a colour coupler (usually contained in thephotographic material) to form image dye. The amount of dye formeddepends on the time of treatment or the availability of colour couplerrather than the amount of silver in the image as is the case inconventional colour development processes. Examples of suitableoxidizing agents include peroxy compounds including hydrogen peroxide,cobalt (III) complexes including cobalt hexammine complexes, andperiodares. Mixtures of such compounds can also be used.

Since the amplifying solution contains both an oxidizing agent and areducing agent it is inherently unstable. That is to say unlike aconventional colour developer solution, amplifier solutions willdeteriorate in less than an hour even if left in a sealed container. Thebest reproducibility for such a process has been obtained by using a"one shot" system, where the oxidant is added to the developer and thesolution mixed and used immediately (or after a short built in delay)and then discarded. This leads to the maximum solution usage possiblewith maximum effluent and maximum chemical costs. As a result the wholesystem is unattractive especially for a minilab environment whereminimum effluent is required. It is believed that it is theseshortcomings that have inhibited commercial use of this process.

Japanese Specification 64/44938 appears to describe such a system inwhich a silver chloride colour material is processed in a low volume ofa single-bath amplifier solution. The processes described thereinhowever fall short of what is required in the fully commercialenvironment for exactly the reasons given above.

Published International Patent Application WO-A-91/12567 (whichcorresponds to British Patent Application No. 9003282.2) describes amethod and apparatus for photographic processing in which a minimumamount of processing solution can be used in a processing tank which isthin and has a low volume. In order to overcome the inherentdeterioration problem due to the instability of the processing solutionsused, the method and apparatus described result in the need for highrecirculation and/or replenishment rates. However, problems associatedwith non-uniform processing of the photographic material may beencountered due to local differences in the concentration of theprocessing solution. Agitation of the processing solution appears toprovide one solution to this problem.

SUMMARY OF THE INVENTION

JP-A-2 135 342 discloses agitation of processing solution in aprocessing tank. In one embodiment, agitation is provided by aplunger-like arrangement in several processing tanks at once. In asecond embodiment, agitation is provided by processing solution beingpumped through a hollow member arranged in the center of the processingtank.

According to one aspect of the present invention, there is providedprocessing apparatus comprising a tank and a plurality of agitationmember's mounted within the tank characterized in that the agitationmembers are positioned in the tank so as to be totally submerged byprocessing solution in the tank and in that the agitation members aremoved into contact with at least the emulsion surface of the materialbeing processed by motion of the material itself.

By this arrangement, the agitation members cause agitation to occur atthe surface of photographic material being processed as it passesthrough the tank thereby producing a more uniform end result.

Advantageously, the members also maintain the position of thephotographic material against one wall of the tank ensuring maximumaccessibility of processing solution to the surface of the materialbeing processed.

Preferably, the agitation members are porous. This enhances thecirculation of the processing solution as it can pass through eachmember as well as around it.

For a better understanding of the present invention, reference will nowbe made, by way of example only, to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectioned side view of a U-shaped processing tankincorporating agitation members constructed according to the invention;

FIG. 2 is a sectioned view through the tank of FIG. 1 on an enlargedscale showing the fixing of one agitation member to the wall of thetank; and

FIG. 3 is similar to FIG. 2, but illustrates a second embodiment of anagitation member constructed in accordance with the present invention.

FIG. 4 is similar to FIG. 1, but illustrates an embodiment comprisingwipers 17 and 30.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a low volume thin tank 10 is shown. The tank 10 is generallyU-shaped with an outer wall 11 and a central block 12 which define apath 13 for photographic material within the tank between an inlet 14and an outlet 15. The outer wall 11 and central block 12 are separatedby a distance T which is approximately 1.5 mm all the way along path 13as shown. A valve denoted by `X` is provided in the base of the tank 10to allow used processing solutions to be drained from the tank.

Photographic material, for example exposed sensitized paper, (not shown)is fed into the tank 10, in the direction of arrow `A`, at the inlet 14and is passes around a lower part 16 of the tank, in the direction shownby arrow `B`, before emerging at the outlet 15. Six agitation members orwipers 17 are positioned at spaced locations 18 around the tank in path13, each agitation member or wiper 17 extending the full width of thetank 10.

FIG. 2 illustrates one of the wiper locations 18 in more detail. Atlocation 18, paper 20 in path 13 is pressed against wall 11 by a wiper17. The wiper 17 is made from a porous material, for example woven nylonfilament. Alternatively, the porous material could be a mesh. One end 21of the wiper 17 is mounted in a recess 22 formed in the central block12. The end 21 of the wiper 17 is fixed in the recess 22 by a plate 23.The plate 23 is fixed relative to the recess 22 by screws 24 (only oneshown) which passes through the plate and into the central block 12. Theplate 23 is not as deep as the recess 22 in which it is positioned, andhas a countersunk hole as shown to allow the screw 24 to lie flush withor slightly above the upper surface of the plate itself. The arrangementof end 21 of wiper 17 and plate 23 in recess 22 is such that each wiperemerges from under the plate 23 at an angle of approximately 45°. Thisarrangement gives the wipers 17 the desired stiffness.

End 25 of wiper 17 is free and is positioned to lie against emulsionsurface 26 of paper 20 or against inner surface 19 of wall 11 when nopaper is present. As the end 25 of wiper 17 contacts the paper 20 beingprocessed, agitation of the processing solution (not shown) in path 13is caused at surface 26 as the paper 20 is moved along path 13. Some ofthe processing solution is carried along under the wiper 17, as shown byarrow `C`, and the remainder of the processing solution, indicated byarrow `D`, passes through the wiper 17 and emerges as indicated by arrow`E`. Some flow of processing solution through the wiper 17 also occursin the region designated as `F`.

The wipers 17 produce agitation by disturbing the laminar layer ofprocessing solution at the surface 26 of the paper 20 whilst allowingsolution to pass through. This action mixes the development by-productswith fresh solution added during replenishment to make the developmentprocess more uniform and a higher density.

The material from which the wiper 17 is made is flexible allowing it totake up the configuration shown in FIG. 2, but of sufficient stiffnessto cause the paper being processed to maintain its position with thebase side of the paper being held against the wall 11. This actionreduces physical damage to the paper and improves solution delivery tothe surface 26 of the paper 20.

It is preferred that surface 27 of central block 12 is roughened toprevent the photographic material adhering to the surface of the block.In this embodiment, the roughening is provided by a layer 28 of meshmaterial which is attached to the surface 27.

A second embodiment of a wiper 30 is shown in FIG. 3. Like parts arereferenced alike but with a letter `a` appended. In this embodiment, end31 of wiper 30 is fixed to the central block 12a by gluing. End 32 isfolded under so that it lies against the central block 12a and notagainst the paper 20a. A portion 33 of the wiper 30 brushes against thesurface 26a of the paper 20a and produces the desired agitation. In thiscase, the end 31 of the wiper 30 extends to lie underneath portion 34(formed by folding back end 32) of an adjacent wiper. This removes theneed for an additional layer of mesh as shown in FIG. 2. As before, thewiper 30 is made of porous material.

In the embodiment shown in FIG. 2, each wiper 17 is made from 61 mesh(holes/inch) woven nylon filament 190 microns thick. Each wiper isapproximately 10 to 15 mm long.

It is preferred that there are sufficient wipers arranged in the tank 10so that the paper 20 passing through the tank encounters between one andtwo wipers per second during a thirty second development time.

The wiper 17 shown in FIG. 2 consists of a fine nylon mesh. It appearsthat the combined `fineness` and stiffness of the wiper is important.Other materials could also be used instead of the mesh. For example, acontinuous sheet of thin plastics or rubber material with holes punchedin it may be used.

Other lengths of wiper 17 may also be found to be equally effective atproducing the desired agitation. If longer wipers are used, it may bethat fewer wipers would be needed as more agitation would be providedover a larger emulsion area. However, there may an optimum maximumlength over which processing solution flow in the tank is restricted.

In the embodiment described with reference to FIG. 2, the free end ofthe wiper which lies against the surface of the material being processedis shaped to be orthogonal to the direction of motion of the materialthrough the tank. Alternatively, the free end of the wiper could beangled to avoid drag lines being formed on the surface of the materialbeing processed.

Instead of wipers as shown in FIGS. 2 and 3, that is, being made ofporous material, they may be made from non-porous material and take theshape similar to the teeth of a comb. Naturally, the teeth of one wiperwould be offset from those of an adjacent wiper so that evendistribution of the processing solution is still obtained.

In the described embodiment of the tank, the wipers are mounted on thecentral block 12 and act to press the photographic material against theinternal surface of outer wall 11. This allows maximum access of theprocessing solution to the surface of the photographic material beingprocessed. In the case where the emulsion surface of the photographicmaterial being processed needs to face the internal surface of outerwall 11 (due to apparatus constraints further along the processingpath), the wipers 17 can be positioned on outer wall 11.

As an alternative, if the photographic material to be processed isdouble-sided, wipers may be arranged on both the internal surface of theouter wall 11 and the surface of the central block 12, the photographicmaterial passing between the wipers as it moves along path 13.

Although the apparatus of the present invention has been described foruse with photographic materials such as sensitized paper, its use is notlimited to such materials only. Wipers can also be used to produceagitation of processing solutions for both single- and double-sidedfilms.

We claim:
 1. Processing apparatus comprising a tank and a plurality ofagitation members mounted within the tank characterized in that theagitation members are positioned in the tank so as to be totallysubmerged by processing solution and in that the agitation members aremoved by motion of the material being processed as at least the emulsionsurface of the material being processed contacts with the agitationmembers.
 2. Apparatus according to claim 1, wherein the agitationmembers are porous.
 3. Apparatus according to claim 2, wherein theporous agitation members comprise 61 mesh (holes/inch) woven nylonfilament.
 4. Apparatus according to claim 3, wherein the filament is 190μm thick.
 5. Apparatus according to claim 1, wherein each agitationmember has an operational length of between 10 and 15 mm.
 6. Theapparatus according to claim 1 further comprising a second plurality ofagitation members mounted within the tank on a side substantiallyopposite from said other plurality of agitation members.